Process for recovering rare-earth oxides



PROCESS non RECQVERING RARE-EARTH oxrnas John Bryant Kasey, Bakersfield,{jaliifi No Drawing. Application August 1, 1956, Serial No. 691,337

8 Claims. (Cl. 75-1) This application for patent constitutes acontinuation of my prior application Serial No. 290,559, Series of 1948,filed May 28, 1952, now abandoned.

This invention relates to a process for enriching the concentration ofrare-earth oxides in an ore or ore concentrate. More particularly, itrelates to a process for enriching the concentration of rare-earthoxides in an ore or ore concentrate containing rare-earthfluo-carbonates, fluorides, oxy-fluorides, bore-fluorides, orsilico-fluorides as values and a gangue consisting chiefly of barite.For the purposes of this application, the term rare-earths is defined aselements Whose atomic numbers lie between 57 and 71 inclusive.

The invention relates more particularly to a process of chemicalconversion of values consisting of rare-earth lino-carbonates,fluorides, oxy-fluorides, boro-fluorides, or silico-fluorides torare-earth oxides, concurrent with the chemical conversion ofsubstantially all the fluorine content of said values to water-solublefluorides which'may thereafter be removed, along with otherwater-soluble impurities, by leaching with water. Further, the inventionrelates to a process for recovering rare-earth oxides in a concentrationof 60% or more from an ore or ore concentrate in which the gangueconsists chiefly of barite, by chemically converting the values torare-earth oxides, concurrently converting substantially all thefluorine content thereof to water-soluble fluorides, separating thelatter and other water-soluble impurities from the former by leachingwith water, and thereafter further concentrating the rare-earth oxidesby gravity separation of barite therefrom.

Prior to this invention, it has not been possible to enrich sufficientlythe concentration of rare-earth oxides in an ore or ore concentratecontaining as values mineral fluo-carbonates, fluorides, oxyfluorides,hero-fluorides, or silico fluorides of rare-earth elements such ascerium or lanthanum, and containing a gangue such as barite. Thedifliculty in such cases is largely that gravity separation is notfeasible, since the values have a specific gravity which is very closeto that of the gangue. For example, the rare-earth fluo-carbonate,bastna site, has a specific gravity of 5.2, while the specific gravityof barium sulfate, barite, is about 4.6. Thus, gravity separation to thenecessary extent has not proved practically feasible. The separation isnecessary if rare-earth oxides are to be prepared from such materials,which oxides are later to be reduced to mixed metals for such purposesas alloying in steel. In such applications, the sulphur content of thebarite would be very detrimental. The separation is also of' importancebecause the removal of the unwanted barite permits a considerablereduction in shipping cost. For these purposes, it is considerednecessary that the concentrate contain a minimum of 60% rare-earthoxides. The production of such an oxide-content concentrate from suchmaterials has heretofore not been accomplished.

-I am aware that the treatment of minerals with various chemicals,thereby changing the specificgravity of Patented Sept. 10, 1957 one ormore of the substances contained therein sufliciently to permit gravityseparation is not generally novel. Thus, in U. S. 1,887,264 (Nov. 8,1932), Grengle treats an ore with sodium bisulfate in the presence of anelectrical current, and this treatment is followed by gravityseparation. In U. S. 2,363,315 (Nov. 21, 1944), Grothe subjects an ironore to a reducing roast, and follows this with gravity separation. Thesetwo inventions involve the treatment of minerals in such a way as tochange the specific gravity of one or more substances, and thereforeshow that this principle is not generally novel, but they do not teachany method for enriching rare-earth oxide concentrations in materials ofthe type I treat.

In my process, I convert rare-earth fluo-carbonates, fluorides,oxy-fluorides, bore-fluorides, or silicofluorides to rare-earth oxidesby an oxidizing roast in the presence of an alkali-metal carbonate,bicarbonate, nitrate, peroxide, or hydroxide. This has the effect ofconverting the rare-earth compounds to oxides, and concurrentlyconverting the fluorine content of the material being treated to awater-soluble alkali-metal fluoride, which is then removed, along withother water-soluble impurities, by leaching with water. Subsequently, 1may separate barite from the rare-earth oxides, if this is necessary inorder to achieve a 60% concentration of rare-earth oxides.

I am aware that roasting in the presence of alkali-metal carbonates isnot generally novel.(see: Westby, U. S. 2,038,399, April 21, 1936), northat roasting in the presence of an alkali-metal nitrate is notgenerally novel (see:- Hammarberg, U. S. 2,123,240, July 12, 1938).However, neither of these patents teaches any method of treatingrare-earth minerals, nor of reacting with fluorinecontaining materials,the former using an alkali simply to neutralize silica in a metallicsilicate ore, and the latter being used to treat iron ore.

I am also aware of the fact that heating a rare-earth material withsodium carbonate, and then leaching with water, is not broadly novel.Urbain, in Annales de Chimie et de physique (7th Series), vol. 19, pages202 206, mentions such a process, in which he treats a materialcontaining rare-earth oxides or complex oxides as values and silica andphosphoric acid as gangue, at a temperature of about 500600 C., withsodium carbonate. However, in Urbains treatment, the reagent does notreact with the values (since they are already in the oxide form), butreacts instead with the gangue, neutralizing the silica and. phosphoricacid. The products by driving off carbon dioxide, thereby greatlyincreasing the specific gravity of the rare-earth materials, so thatgravity separation of gangue may thereafter be accomplished. In thepresent application, however, I am able' to treat rare-earth ores or oreconcentrates containing compounds which are not convertible to oxidesmerely upon heating, since they also contain fluorine. Thus, my presentinvention goes one step further than my previously patented invention,in that it makes it possible for the first time to produce highrare-earth oxide concentrations from materials containing as valuesrare-earth lino-carbonates, fluorides, oxy-fluorides, bore-fluorides, or

. silico-fluorides, and as gangue chiefly barite,

V 60% oxides.

Thus, an object of the present invention is to convert rare-earthflue-carbonates, fluorides, oxy-fluorides, borofluorides, orsilico-fluorides to rare-earth oxides by treat- 'ment"at elevatedtemperature under oxidizing conditions with an alkali-metal carbonate,bicarbonate, nitrate, per-' oxide, or hydroxide, concurrently convertingsubstantially all the fluorine content of the rare-earth compounds towater-soluble alkali-metal fluorides, which can then be removed byleaching with water. 'A further object is to convert rare-earthflue-carbonates, fluorides, oxy-fluo- 1 rides to rare-earth oxides bytreatment atlelevated temperature under oxidizing conditions with :analkali-metal carbonate, bicarbonate, nitrate, peroxide, or hydroxide;concurrently converting substantially all the fluorine cone? tent of therare-earth compoundsto water-soluble alkali" metal fluorides,subsequently removing suchlfluorides by leaching with water, and thenseparating barite from the rare-earth oxides by gravity separation.

A further object is to permit the separation of the valuable mineralbastnasite from the less desirable mineral barite, thereby producing aconcentrate containing at least 60% rare-earth oxides, hereinafterreferred to as REG: Another object is to produce a concentratepractically free of barite and consisting virtually entirely ofrareearth oxides. A further object is to produce a concentrate higher intotal R-EO content .than is possible even if the concentrate consistedof pure bastnasite and no barite gangue. Still another object is toconvert the. fluorine content of any of the above-mentioned fluoridecompounds into a useful form such as sodium fluoride.

Other objects and advantages of the invention will more fully appearfrom'the following description, Wherein are disclosed preferred modesof'carrying out the invention.

In the preferred mode of carrying out the present invention, thestarting material is a mixed concentrate'of bastnasite and barite,lighter gangue minerals having.

. been removed during a prior milling operation. This primary, mixedconcentrate contains a widely variable. percentage of REO as bastnasite,depending on relative ratios of light gangue and barite, but containsless than To such a mixed concentrate which has been dried, weighed andanalyzed for REO and fluorine content there'is added'an amount of drysodium carbonate equivalent to the fluorine content plus some excess(preferably to 100% excess), and the Whole is mixed thoroughly. Themixture is then subjected to a temperature within the range ofapproximately 8501000.

C. for aperiod of seve'ralhours. The reaction which ensues progressesquietly and results in the formation of water-soluble sodium fluorideand oxides of the rare earths. The mass on cooling assumes a more 'or.less brick red color. Upon cooling, the mixture, which has lost aconsiderable part of its weight because of the evolution of carbondioxide gas, is leached and washed with water to remove the solublesodium fluoride mixed with a small quantity of sodium sulphate.Thelatter is formed by partial decomposition of the barite". 1

Since the difierence in weight between the untreated mixed concentrateand the reacted and washed-concentrate may vary from-about 5% to 20%,depending on the percentage of duo-carbonate present (the CO2 of whichis driven off) the resultant percentage of REO in the washed concentratewill be increased proportionately. Should the washed concentrate REOcontent be below standard, i. e. below 60%, then its REO content can beincreased'by slurrying with water to 5 to solids, feeding it onto agravity concentrating table, and washing the barite (spe'-" cificgravity 4.6) into the tailings and away from the REO (specific gravity7.0). The latter step of separating the barite by tabling yields aconcentrate with maximum REO.

The sodium fluoride-sodium sulphate leaching water and wash water arefurther treated for the recovery of the sodium fluoride as such or ascalcium fluoride byprecipitation with a calcium salt.

To illustrate more clearly my invention, the following is a typicalexample: Fifty grams of a mixed bastnasitebarite concentrate,practically calcite-free and analyzing 59.6% REO, 3.18% fluorine, and12% barite, were ground to minus 150 mesh and thoroughly mixed with 7grams of dry, light anhydrous sodium carbonate (57.6% excess). Themixture was placed in an iron crucible, and subjected to a temperatureof 850 C. in an electric muffle furnace for two hours. The reactionbetween the bastnasite and sodiumpcarbonate proceeded quietly andwithout any visible evidence of activity, although carbon dioxide wasevolved from the porous mass. Sodium fluoride and rare-earth oxides werefor-med simultaneously. At the conclusion of the two-hour period, thelightly sintered product was cooled and placed in 200 cc. of water andleached for two hours. The residue of rareearth oxides and barite wasfiltered and washed free of sodium fluoride and sodium sulphate. Thewashed and dried rare-earth. oxides and barite now weighed 3939 grams,indicating a loss of 10.61 grams or 21.2%,.due to loss of carbon dioxideand solution of fluorine. The REO content of this rare-earth-bariteresidue was 75.5%, an increase of 26.6% in REO content due to heattreatment and reaction with the added sodium carbonate. The specificgravity of the rare-earth oxides was now 7.0. The diflerence in specificgravity between them and the barite therefore enabled their separationby gravity concentration, the much lighter barite being easily washedinto the tailings. Oxides obtained. by such a concentration processanalyzed 96.6% REO and 2.25% barite, with recovery averaging 93%; a 7

While I have specifically employed. sodium carbonate in the aboveexample, it should be understood that certain other substancesmay besimilarly used and sub stituted for it as equivalents, singly or mixed,in effecting the decomposition. and conversion of bastnasite andtheother above-enumerated fluorine minerals to the oxide form., Suchequivalents of sodium carbonate include the carbonates, bicarbonates,nitrates, peroxides, and hydroxides of the alkali-metals. Thesesubstances have in common with each other the property of beingconverted to alkali-metal oxides upon heating within the range 8501000C. In addition any other alkali-metal or alkali-metal compound which isconverted to an alkalimetal oxide upon heating Within the range of8504000 C. in atmospheric air or in the presence of an oxidizing agentconstitutes an equivalent of the reagents mentioned above. This includesthe alkali-metal elements sodium, potassium, and lithium, and theirnitrites and cyanides.

Some examples of the practice of my invention when equivalents areemployed instead of using sodium carbonate a's'the reagent follow. Ineach of these examples, a

mixed bastnasite-barite concentrate, practically calcite free andanalyzing 59.6% REO, 3.18% fluorine, and

12% barite, groundto minus 150 mesh, was treated. The method oftreatment was essentially the same as that employed in the exampleabove, wherein sodium carbonate was employed as the reagent.

In each case, the excess of reagent was 57.6%, and the recovery offluorine in the filtrate was found to be essentially complete.- V

While certain novel features of this invention have been disclosed andare pointed out in the following claims, it

will be understood that various omissions, substitutions," and changesmay bemade'by those skilled in the art without departing from thespiritof theinventio'n.

I claim:

1. A process for recovering rare-earth oxides in a concentrationexceeding approximately 60% from a solid rare-earth-containing materialcontaining a mixture of values which comprise minerals selected from thegroup consisting of rare-earth fluo-carbonates, fluorides, oxyfluorides,bore-fluorides, and silico-fluorides, and a gangue consisting chiefly ofbarite, which comprises the novel steps of: heating saidrare-earth-containing material under oxidizing conditions to atemperature within the range of approximately 850-1000 C. in thepresence of a reagent selected from the group consisting of thecarbonates, bicarbonates, nitrates, peroxides, and hydroxides of thealkali metals to form water-soluble alkali-metal fluoride and sulphatesalts and to convert the rare-earth compounds to oxides, the amount ofsaid reagent being substantially chemically equivalent to the fluorinecontent of said rare-earth-containing materials; continuing said heatinguntil substantially all the values in said rare-earth-containingmaterial have been converted to rare-earth oxides and substantially allthe fluorine content of said values has been converted to solublealkali-metal fluorides; and thereafter leaching the treated materialwith water to remove the soluble alkali-metal fluorides and sulfatestherefrom.

2. A process for recovering rare-earth oxides in a concentrationexceeding approximately 60% from a solid rare-earth-containing materialcontaining a mixture of values which comprise minerals selected from theconsisting of rare-earth flue-carbonates, fluorides, oxy-fiuorides,

bore-fluorides, and silico-fluorides, and a gangue consisting chiefly ofbarite, which comprises the novel steps of: heating saidrare-earth-containing material under oxidizing conditions to atemperature within the range of approximately 8501000 C. in the presenceof a reagent selected from the group consisting of the carbonates,bicarbonates, nitrates, peroxides, and hydroxides of the alkali metalsto form water-soluble alkali-metal fluoride and sulphate salts and toconvert the rare-earth compounds to oxides, the amount of said reagentbeing substantially chemically equivalent to the fluorine content ofsaid rareearth-containing materials; continuing said heating untilsubstantially all the values in said rare-earth-containing material havebeen converted to rare-earth oxides and substantially all the fluorinecontent of saidvalues has been converted to soluble alkali-metalfluorides; there after leaching the treated material with water toremove the soluble alkali-metal fluorides and sulfates therefrom; andthereafter further concentrating the rare-earth oxides by gravityseparation of barite therefrom.

3. The process of claim 1, wherein the rare-earth is selected from thegroup consisting of cerium, lanthanum, and mixtures thereof.

4. The process of claim 2, wherein the rare-earth is selected from thegroup consisting of cerium, lanthanum, and mixtures thereof.

5. The process of claim 1, wherein said reagent is sodium carbonate.

6. The process of claim 2, wherein said reagent is sodium carbonate.

7. The process of claim 1, wherein the rare-earth is selected from thegroup consisting of cerium, lanthanum, and mixtures thereof, and whereinsaid reagent is sodium carbonate.

8. The process of claim 2, wherein the rare-earth is selected from thegroup consisting of cerium, lanthanum, and mixtures thereof, and whereinsaid reagent is sodium carbonate.

References Cited in the file of this patent UNITED STATES PATENTS1,546,854 Miller July 21, 1925 1,887,264 Grenagle Nov. 8, 1932 2,038,399Westby Apr. 21, 1936 2,123,240 Hammarberg July 12, 1938 2,363,315 GrotheNov. 21, 1944 OTHER REFERENCES Annalles de chimie et de Physique (7thseries), vol. 19, pages 202-206.

Comprehensive Treatise of Inorganic and Theoretical Chemistry, byMellor, vol. 5, page 545; published in 1924 by Longmans, Green andCompany, New York, N. Y.

1. A PROCESS FOR RECOVERING RARE-EARTH OXIDES IN A CONCENTRATIONEXCEEDING APPROXIMATELY 60% FROM A SOLID RARE-EARTH-CONTAINING MATERIALCONTAINING A MIXTURE OF VALUES WHICH COMPRISE MINERALS SELECTED FROM THEGROUP CONSISTING OF RARE-EARTH FLUO-CARBONATES, FLUORIDES, OXYFLUORIDES,BORO-FLUORIDES, AND SILICO-FLOUIDES, AND A GANGUE CONSISTING CHOIEFLY OFBARITE, WHICH COMPRISES THE NOVEL STEPS OF: HEATING AND RERE-EARTHCONTAINING MATERIAL UNDER OXIDIZING CONDITIONS TO A TEMPERATURE WITHINRANGE OF APPROXIMATELY 850-1000*C. IN THE PRESENCE OF A REAGENT SELECTEDFROM THE GROUP CONSISTING OF THE CARBONATES, BICARBONATES, NITRATES,PEROXIDES, AND HYDROXIDES OF THE ALKALI MATALS TO FORM WATER-SOLUBLEALKALI-METAL FLUORIDE AND SULPHATE SALTS AND CONVERT THE RARE-EARTHCOMPOUNDS TO OXIDES, THE AMOUNT OF SAID REAGENT BEING SUBSTANTIALLYCHEMICALLY EQUIVALENT TO THE FLUORINE CONTENT OF SAIDRARE-EARTH-CONTAINING MATERIAL; CONTAINING SAID HEATING UNTILSUBSTANTIALLY ALL THE VALUES IN SAID RARE-EARTH-CONTAINING MATERIAL HAVEBEEN CONVERTED TO RARE-EARTH OXIDES AND SUBSTANTIALLY ALL THE FLOURINECONTENT OF SAID VALUES HAS BEEN CONVERTED TO SOLUBLE ALKALI-METALFLUORIDES; AND THEREAFTER LEACHING THE TREATED MATERIAL WITH WATER TOREMOVE THE SOLUBLE ALKAL-METAL FLUORIDES AND SURFACE THEREFROM.